The herpes group of viruses which include cytomegalovirus (CMV), a member of Epstein-Barr virus (EBV), Varicella Zoster virus (VZV), herpes simplex viruses (HSV-1, HSV-2) and human herpes viruses HHV6, HHV7, and HHV8, is recognized as an important pathogen in patients with AIDS. The virus often contributes to the immunosuppression observed in such patients and may cause disseminated disease involving the lungs, gastrointestinal tract, central nervous system, or eves. CMV retinitis is recognized as a major cause of blindness in patients with AIDS. Also, human cytomegalovirus (HCMV) infection is a major cause of death in AIDS patients. Currently, there are only two approved drugs, ganciclovir, an acyclic guanine nucleoside, and foscarnet, for its treatment. Ganciclovir has exhibited bone marrow suppression as a serious side effect and resistant strains have also been isolated. Foscarnet presents side effects that are associated with its administration such as reversible renal dysfunction, thrombophlebitis at the infusion site, headaches and anemia. Also, foscarnet is not orally bioavailable, limiting its utility in clinical treatment. It is poorly soluble, and large doses are required because of its relatively low potency. Thus, the development of patent and non-toxic anti-CMV agents is therefore highly desirable.
Since their discovery in 1986, the acyclic phosphonate nucleotide analogs have generated considerable attention as broad spectrum antiviral agents. The guanine analogues HPMPG and PMEG, the adenine analogues HPMPA, and the cytosine analogue HPMPC have been shown to exhibit good anti-HCMV activity and HSV activity. PMEA has also demonstrated in vitro activity against retroviruses such as the human immunodeficiency virus (HIV), as well as DNA viruses such as herpes simplex virus (HSV), and in vivo activity against murine cytomegalovirus (CMV). 
Unfortunately, in general these compounds present problems in cytotoxicity, particularly, PMEG which is very cytotoxic.
All human herpesviruses have a worldwide distribution and are amongst the most difficult human pathogens to control. Currently, considerable efforts are being directed towards the development of vaccines and antiviral agents that will be active against herpesviruses, particularly Herpes Simplex viruses HSV-1 and HSV-2, and Varicella Zoster virus (VZV). A number of nucleoside and nucleotide derivatives are, active against primary and recurrent HSV infection; of these, acyclovir is the most used drug. However, among patients with AIDS, acyclovir-resistant HSV-2 may lead to chronic progressive infections. There is therefore a need for development of potent and non-toxic agents against Herpes viruses.